Field of the Invention
The present invention relates to a radiation-sensitive resin composition, a polymer and a method for forming a resist pattern.
Discussion of the Background
In the field of microfabrication for producing integrated circuit elements, a lithography technique that allows for microfabrication at a level of no greater than 0.10 μm (subquater-micron level) has been desired in order to attain a higher integrity. However, according to conventional lithography techniques, a near ultraviolet ray such as i-ray is used as a radioactive ray; therefore, microfabrication at the level described above has been extremely difficult. Thus, in order to allow for microfabrication at the aforementioned level, development of lithography techniques carried out using a radioactive ray with a shorter wavelength have been performed. The radioactive ray with a shorter wavelength may involve, for example, bright line spectra of a mercury-arc lamp, far ultraviolet rays such as excimer laser, X-ray, electron beams, and the like. Of these, KrF excimer laser (wavelength: 248 nm) and ArF excimer laser (wavelength: 193 nm) have attracted attention.
As the excimer laser has attracted attention, a number of materials of resist films for excimer laser have been proposed. Such materials include, for example, compositions (hereinafter, may be also referred to as “chemically amplified resists”) that contain a component having an acid-dissociable group, and a component (hereinafter, may be also referred to as “acid generator”) that generates an acid upon irradiation with a radioactive ray (hereinafter, may be also referred to as “exposure”), whereby a chemical amplification effect thereof is used, and the like (see Japanese Unexamined Patent Application, Publication No. 2008-308545 and Japanese Unexamined Patent Application, Publication No. 2008-308546). In this composition, the acid-dissociable group present in the resin is dissociated due to the action of an acid generated upon exposure, thereby rendering the resin have an acidic group or the like. As a result, formation of a desired resist pattern is enabled since an exposed region of the resist film becomes easily soluble in an alkaline developer.
However, in the field of microfabrication, formation of a still finer resist pattern (for example, fine resist patterns having a line width of about 45 nm) has been desired. A method for enabling a still finer resist pattern to be formed may involve, for example, decrease in the wavelength of the light source of an exposure system, increase in the number of numerical apertures (NA) of the lens, and the like. In this regard, decrease in the wavelength of the light source necessitates a novel exposure system, which would be expensive. In addition, since a trade-off lies between the resolution and the focal depth when the numerical aperture of lens is increased, it may be disadvantage in that the focal depth decreases even if resolution can be improved.
Accordingly, a method referred to as liquid immersion lithography was recently reported as a lithography technique that can solve such a problem. In this method, a liquid for liquid immersion lithography (for example, pure water, fluorine-based inert liquid, etc.) is placed between the lens and the resist film (on the resist film) during exposure. According to this method, light path-space of the exposure, which has been conventionally filled with inert gas such as air or nitrogen, is filled with a liquid for liquid immersion lithography having a refractive index (n) greater than that of the air and the like; therefore, even if the light of exposure similar to that of a conventional type is used, an effect similar to that achievable when the light of exposure has a shorter wavelength can be achieved. More specifically, higher resolving abilities can be attained, and decrease in the focal depth is enabled.
Therefore, according to such liquid immersion lithography, formation of a resist pattern is enabled at low costs, with superior ability of high resolution and also with favorable focal depth, even in the case in which a lens mounted in preexisting apparatuses is used. Thus, a large number of compositions which may be used in liquid immersion lithography have been reported (see pamphlet of PCT International Publication No. 2007/116664, Japanese Unexamined Patent Application, Publication No. 2005-173474 and Japanese Unexamined Patent Application, Publication No. 2006-48029).